1. Field of the Invention
The present invention relates in general to heating fluidized bed gasification systems, and in particular to a new and useful system and method for gasifying residual waste liquor.
2. Description of the Related Art
In certain processes, for instance, the Kraft paper making process, a residual waste liquor such as black liquor byproduct produced in this process is gasified using a fluidized bed. The fluidized bed comprises a granular bed material and a fluidizing medium. The black liquor is gasified by providing a heat input to the fluidized bed. The heat input can be provided by heat transfer surfaces such as heat exchanger tubes which are located in the bed material. U.S. Pat. No. 5,059,404 describes one such indirectly heated process using pulse combustion. Some methods require the addition of heat input directly to the bed material itself through the consumption of product being gasified.
A common problem associated with heat exchanger tubes located in the material bed is that the tubes are subjected to fouling and corrosion due to their proximity with the fluidizing bed material. A major problem associated with the direct heat input to the material bed is that potential high temperature spots created through the direct heat input sometimes result in the formation of smelt, i.e. molten inorganic constituents resulting from the reduction of black liquor in the bed material.
There is a need for an improved system and method for gasifying residual waste liquor that does not foul or corrode heat transfer surfaces and avoids smelt formation problems.